Fix data race in loadAlignmentPatternLoc (#104)

* Fix data race in loadAlignmentPatternLoc

* Add test for loadAlignmentPatternLoc with concurrent access

* go test with -race flag

.github/workflows/go.yml

@@ -34,21 +34,21 @@ jobs:
         stable: false
 
     - name: Build
-      run: go build -v ./...
+      run: go build -v -race ./...
 
     - name: Test qrcode
       working-directory: .
-      run: go test -v ./...
+      run: go test -v -race ./...
       continue-on-error: false
 
     - name: Test writer/standard
       working-directory: ./writer/standard
-      run: go mod tidy && mkdir testdata && go test -v ./...
+      run: go mod tidy && mkdir testdata && go test -v -race ./...
       continue-on-error: false
 
     - name: Test writer/terminal
       working-directory: ./writer/terminal
-      run: go mod tidy && mkdir testdata && go test -v ./...
+      run: go mod tidy && mkdir testdata && go test -v -race ./...
       continue-on-error: false
 
     - name: Upload coverage reports to Codecov

version.go

@@ -4,6 +4,7 @@ import (
 	"errors"
 	"log"
 	"strconv"
+	"sync"
 
 	// "github.com/skip2/go-qrcode/bitset"
 	"github.com/yeqown/reedsolomon/binary"
@@ -353,7 +354,8 @@ var (
 		40: {6, 30, 58, 86, 114, 142, 170},
 	}
 
-	alignPatternCache = map[int][]loc{}
+	alignPatternCache   = map[int][]loc{}
+	alignPatternCacheMu sync.Mutex
 )
 
 // loc point position(x,y)
@@ -367,6 +369,10 @@ func loadAlignmentPatternLoc(ver int) (locs []loc) {
 	if ver < 2 {
 		return
 	}
+
+	alignPatternCacheMu.Lock()
+	defer alignPatternCacheMu.Unlock()
+
 	var ok bool
 	if locs, ok = alignPatternCache[ver]; ok {
 		return

version_test.go

@@ -4,6 +4,7 @@ import (
 	"math/rand"
 	"reflect"
 	"strings"
+	"sync"
 	"testing"
 
 	"github.com/stretchr/testify/require"
@@ -231,6 +232,22 @@ func Test_binarySearchVersion_all(t *testing.T) {
 	}
 }
 
+func Test_loadAlignmentPatternLoc_concurrentAccess(t *testing.T) {
+	var wg sync.WaitGroup
+
+	for ver := 2; ver <= _VERSION_COUNT; ver++ {
+		wg.Add(1)
+
+		go func(v int) {
+			got := loadAlignmentPatternLoc(v)
+			assert.NotEmpty(t, got)
+			wg.Done()
+		}(ver)
+	}
+
+	wg.Wait()
+}
+
 // // go test -run=NONE -bench . -count 10 > new/old.txt
 func Benchmark_loadVersion_top(b *testing.B) {
 	for i := 0; i < b.N; i++ {